The present invention relates generally to systems and methods for minimizing adverse affects of network transfer latency on packet data transmission, and more specifically to a system and method for minimizing the adverse affects of network transfer latency that reduces a perceived quality degradation of the packet data transmission.
Computerized network interface devices are frequently employed to link different types of computer networks to one another. For example, such network interface devices may be configured to operate as a “gateway” device to translate data traffic from one protocol to another, as an “endpoint” device to store and forward fax data during a fax “store-and-forward” session, or as any other suitable device capable of linking two (2) computer networks together.
One conventional computer network arrangement includes a network interface device configured to link a packet switched network such as the Internet to a synchronous circuit switched network such as the Public Switched Telephone Network (PSTN). The interface device typically performs packet-based media processing on packets of sampled and possibly compressed data transmitted across the packet switched network. For example, the packet data may comprise audio data including samples of voice or music, fax data, modem data, and/or telephony signaling tones. Further, the interface device may perform operations for packet data de-jittering, line echo canceling, packet data decoding, and/or sample clock regenerating, among other possible packet-based media processing operations.
A shortcoming of transmitting packet data across packet switched networks is that it is often difficult to assure reliable delivery of the packet data. For example, when transmitting packet data from a source node in a packet switched network to a network interface device such as a gateway or endpoint device via at least one intermediate node in the packet switched network, the intermediate node may at least temporarily stop accepting data due to traffic congestion, network maintenance, or node failure, and cause the packet data to take an alternate route to the interface device. As a result, respective packets may take different routes from the source node to the interface device, thereby making the packet data subject to varying network transfer latencies. This can make it hard to assure that the packet data will be received by the interface device at a specified rate and in the proper sequence, and that no packet data will be inadvertently dropped during transmission.
Varying network transfer latencies can also influence a user's perception of the quality of the packet data transmission in different ways, depending on the type of information content of the packet data. For example, in the event the packet data contains voice samples, network transfer latencies that cause the voice samples to be delayed by more than about 200 msecs may significantly degrade the natural dynamics of a telephone conversation. Moreover, in the event the packet data contains fax data, network transfer latencies that cause the fax data samples to be received in an incorrect sequence or cause at least one of the data samples to be dropped may lead to undesirable bit errors in a facsimile output.
In an attempt to minimize the adverse affects of network transfer latency, the network interface device included in the conventional computer network arrangement typically buffers the packet data. For example, the interface device may temporarily store the packet data received from the packet switched network in a buffer until a predetermined amount of the packet data samples are received and stored, sequentially sort and decode the packet data samples, and transmit the sorted and decoded packet data samples to the user's location in the synchronous circuit switched network. However, such packet data buffering typically introduces additional delay that can further degrade the user's perception of the data transmission, especially when the type of information content of the packet data is voice or music.
It would therefore be desirable to have a system and method for minimizing adverse affects of network transfer latency on packet data transmitted across packet switched networks. Such a system and method would minimize the adverse affects of network transfer latency with reduced degradation of a user's perception of the quality of the data transmission.